Periodontal probes are used to test the depth of a pocket which exists between a tooth and a gum. The pocket is formed as a result of progressive gingival inflammation. Once formed, the periodontal pocket provides a sheltered environment for pathogenic microbial colonies, which may cause further connective tissue destruction. The depth measurement indicates whether periodontal disease is present and to what extent; the deeper the pocket, the less attachment there is between the tooth and gum and more likely it is that treatment is required.
Typical periodontal probes, shown for example in U.S. Pat. Nos. 4,768,952, 4,886,454, and 4,764,114, use a needle-like tip. The tip is inserted until the bottom of the pocket is reached, with the tester relying on the resistance to insertion to feel the bottom of the pocket. The tip usually has markings to indicate the depth of the pocket. Pocket depths over about three millimeters indicate that treatment should be undertaken. Two or three readings may be taken per tooth and a history developed to note changes in pocket depth to determine if progressive pocket enlargement is apparent.
A problem with periodontal probing is that, to be accurate, the pressure used to push down the probe tip into the pocket must be the same for each test. In addition, the force applied must be less than would cause the tip to pierce the pocket, damaging the tissue and giving an erroneous reading. If different pressure is applied at different locations or during subsequent probing, the readings will vary and the test results become meaningless.
The World Health Organization has determined that a pressure of about 20 grams should be used as the standard insertion pressure. This is the level at which the probe overcomes the resistance caused by the gum mating with the tooth, yet prevents the probe tip from piercing the bottom of the periodontal pocket. This is a very low value compared to the amount of pressure which could be applied during insertion and it is very difficult to feel when that level of pressure has been reached. By monitoring probing done during a typical examination, it was determined that testers routinely applied double or triple this amount of force without being aware of it.